Radio frequency identification is a technology by which electromagnetic waves are transmitted from a reader device to an RFID tag. When the tag is in the interrogation zone of the reader, identifying information of the object is transmitted by the tag to the reader. The RFID tag is attached to or enclosed within an object or container and can be read by the reader without the object being contacted.
An RFID tag typically includes an IC chip with control logic, and an antenna for radio communication. Active tags refer to those that have an internal power source; passive tags refer to those that don't have an internal power source. Active tags can transmit radio frequency information whether or not they are within the interrogation zone of an RFID reader. Passive tags are inductively powered by the radio frequency waves received from the RFID reader, and transmit, or “reflect,” a modulated signal containing identification information. Active tags are able to transmit much more information than passive tags. However, even passive tags are able to transmit on the order of several kilobits of information.
RFID technology is well known and is in widespread use in many different industries, including the shipping industry to track packages, the retail industry for theft control and inventory tracking, and the veterinary field for “microchipping” animals, such as cats, dogs, and livestock. Many retailers require that RFID tags be affixed to product delivered from their suppliers to help with the burdensome and repetitive tasks associated with inventory control. With the use of hand held and automated RFID scanners, retailers are cutting the time and man power required to perform these tasks to a fraction of the effort that is currently required with bar code readers and manual recording of inventory. However, many products, particularly in the high-tech component industries, are already tightly packed with functional items such as openings needed for airflow, externally accessible components (such as fans and hard drives), operator panels and branding. In many cases, affixing an additional functional element to the enclosure would prove difficult.
The form factors of RFID tags vary greatly. The tag can range from the size of a pin head to several square inches. Although factors such as power and durability influence form factor, a major factor is antenna size. Antenna size is primarily determined by the frequency range in which the tag operates. Low frequency (LF) tags operate at about 125 kHz and typically have a small ferrite-coil antenna. A typical form factor for LF RFID tags is a key fob, such as those used at certain gas stations to activate a gas pump. High frequency (HF) RFID tags operate at 13.56 MHz. The typical antennas on these tags consists of several flat windings inlayed on label stock forming a circle, square, or rectangle on the order of one to two inches square. Ultra-high frequency (UHF) RFID tags operate in a range between 860-940 MHz. The typical antennas on these tags consist of an antenna inlaid on label stock, with an overall dimension from about a half-inch square to one inch by three inch rectangle.
The radiation performance of certain antennas used in RFID tags, such as several configurations used with HF and UHF RFID tags, can be enhanced by placing the antenna very close to a flat conducting thin metal plate. The thin metal plate, referred to as a ground plane, can have dimensions approximately equal to the antenna, and can be fabricated as part of the tag. The ground plane, made of a thin metallic layer, is separated from the antenna by a dielectric material.
A type of RFID tag referred to as a “smart label” incorporates an RFID tag into a traditional label. A smart label typically has human readable text and graphics and/or bar code information printed on label stock that incorporates RFID technology. This allows the smart label information to be read by a variety of technologies, including RFID readers, bar code readers, and simple human sight.